This whole igneous area, which includes the newly discovered mountains and oases of Arkenu and Ouenat, is possibly of limited extent, and occurs in, and is possibly surrounded by, a much wider expanse of Nubian Sandstone, in a similar manner to several other such areas already shown on the 1:1,000,000 geological map of Egypt.
Judging from other known similar occurrences where igneous rocks appear surrounded by Nubian Sandstones, we may infer that the latter were deposited upon the ancient igneous rocks which subsequently rose vertically, bending the superincumbent strata over and round them, possibly only to a slight degree in this instance, as none of the photographs show very highly dipping rocks.
On leaving Ouenat for Erdi the igneous area is soon left behind. The actual junction between it and the Nubian Sandstone (which again forms the surface rock) occurs at a point about 20 km. south of Ouenat, and the aspect of the country again changes from the more uneven weathering of the igneous range of grays and browns to brilliant colorings of the Nubian Sandstone which forms a long series of prominent escarpments rising to heights bordering on 1000 meters above the sea between Enebah and Kuttum, after which the ground begins to fall, until El Fasher is reached, where the ground-level is only about 700 or 800 meters in height.
Summary.—The several interesting geological features suggested by the recent expedition may be summarized as follows:
1. That Miocene rocks extend southward, to or near the twenty-seventh degree of north latitude, forming a large bay bordered by older rocks.
2. That the Miocene rocks, resting here apparently upon or against Nubian Sandstones, seem to follow the same conditions noticed first by Dr. Hume in the Gulf of Suez region, namely, that they rest upon older and older formations the further southward they are found; in other words, that prior to the deposition of the Miocene there was a time of denudation which was more effectual in the south than in the north, owing to the fact that in the south was an area of greater uplift.
3. That a large area of Nubian Sandstone (Cretaceous) exists south of this latitude.
4. That a newly discovered range of igneous rocks in the Arkenu Hills exists well inside Egyptian territory, and possibly entirely within this Nubian Sandstone area, or connected as a tongue to a larger igneous massif lying in the south.
5. That the Cretaceous rocks (younger than the Nubian Sandstone) which appear on the colored Geological Map of Egypt further to the northeast, possibly do not occur along the route traversed, having been concealed beneath “sand and alluvium” areas.
List of Specimens Collected by Ahmed Mohammed Hassanein Bey in His Expedition from Sollum to Darfur